Laboratory measurements of wave pressures due to plunging breakers were made on a 6-in. diam semicylindrical tube simulating a prototype concrete structure designed to be placed parallel to the coastline in the surf zone to intercept offshore transport of bean materials and thus preserve the beach. It was found during the wave uprush, that an impact pressure of short duration was recorded at the front of the tube, followed by smoother pressure variations in time. During the wave downrush, the volume of water transported across the tube flowed back under gravity. The pressure distribution on the beach side of the tube was relatively steady in the flow reversing process. The impulse-momentum theory was applied to investigate the behavior of impact pressures. The pressure distribution on the tube surface during the wave downrush was treated as a quasisteady case in which the Bernoulli principle for steady state condition applies.